Portable computing devices, for example Portable Navigation Devices (PNDs), which include GPS (Global Positioning System) signal reception and processing functionality are well known and are widely employed as in-car or other vehicle navigation systems.
In general terms, a modern PND comprises a processor, memory, and map data stored within said memory. The processor and memory cooperate to provide an execution environment in which a software operating system can be established, and additionally it is commonplace for one or more additional software programs to be provided to enable the functionality of the PND to be controlled, and to provide various other functions.
Typically, these devices further comprise one or more input interfaces that allow a user to interact with and control the device, and one or more output interfaces by means of which information may be relayed to the user. Illustrative examples of output interfaces include: a visual display and a speaker for audible output. Illustrative examples of input interfaces include: one or more physical buttons to control on/off operation or other features of the device (which buttons need not necessarily be on the device itself but could be on a steering wheel if the device is built into a vehicle), and a microphone for detecting user speech. In one particular arrangement, the output interface display may be configured as a touch sensitive display (by means of a touch sensitive overlay or otherwise) additionally to provide an input interface by means of which a user can operate the device through the display.
PNDs of this type also include a GPS antenna by means of which satellite-broadcast signals, including location-related data, can be received and subsequently processed to determine a current location of the device.
PNDs of this type can be mounted on the dashboard or windscreen of a vehicle, but can also be formed as part of an on-board computer of the vehicle radio or indeed as part of the control system of the vehicle itself. The navigation device may also be part of a hand-held system, such as a PDA (Portable Digital Assistant), a media player, a mobile phone or the like, and in these cases, the normal functionality of the hand-held system is extended by means of the installation of software on the device to perform both route calculation and navigation along a calculated route.
In the context of a PND, once a route has been calculated, the user interacts with the navigation device to select the desired calculated route, optionally from a list of proposed routes. Optionally, the user can intervene in, or guide the route selection process, for example by specifying that certain routes, roads, locations or criteria are to be avoided or are mandatory for a particular journey. The route calculation aspect of the PND forms one primary function, and navigation along such a route is another primary function.
During navigation along a calculated route, it is usual for such PNDs to provide visual and/or audible instructions to guide the user along a chosen route to the end of that route, i.e. the desired destination. It is also usual for PNDs to display map information on-screen during the navigation, such information regularly being updated on-screen so that the map information displayed is representative of the current location of the device, and thus of the user or user's vehicle if the device is being used for in-vehicle navigation.
Whilst it is known for the device to perform route re-calculation in the event that a user deviates from the previously calculated route during navigation (either by accident or intentionally), a further important function provided by the device is automatic route re-calculation in the event that real-time traffic conditions dictate that an alternative route would be more expedient. The device is suitably enabled to recognize such conditions automatically, or if a user actively causes the device to perform route re-calculation for any reason.
In this respect, the device can continually monitor road and traffic conditions, and offer to or choose to change the route over which the remainder of the journey is to be made due to changed conditions associated with the initially selected route. Real time traffic monitoring systems, based on various technologies (e.g. mobile phone data exchanges, fixed cameras, GPS fleet tracking) are being used to identify traffic delays and to feed the information into notification systems, for example a Radio Data System (RDS)—Traffic Message Channel (TMC) service.
Hence, traffic-related information is of particular use when calculating routes and directing a user to a location. In this respect, and as suggested above, it is known to broadcast traffic-related information using the RDS-TMC service supported by some broadcasters. In the UK, for example, one known traffic-related information service is broadcast using the frequencies allocated to the station known as “Classic fm”. The skilled person should, of course, appreciate that different frequencies are used by different traffic-related information service providers.
A PND, provided with an RDS-TMC receiver for receiving an RDS data broadcast, can decode the RDS data broadcast and extract TMC data included in the RDS data broadcast. Such Frequency Modulation (FM) receivers need to be sensitive. For many PNDs currently sold, an accessory is provided comprising an RDS-TMC tuner coupled to an antenna at one end thereof and a connector at another end thereof for coupling the RDS-TMC receiver thereof to an input of the PND.
Devices of the type described above, for example the 920 GO model manufactured and supplied by TomTom International B.V., which support use of the above-described antenna, support a process of enabling users to navigate from one location to another, in particular using traffic-related information. Such devices are of great utility when the user is not familiar with the route to the destination to which they are navigating.
However, the effectiveness of such devices can sometimes depend upon the effectiveness of the antenna and/or any associated circuitry employed. In this respect, in the field of antenna design, a number of antenna structures are known to have varying degrees of suitability in relation to receipt of RDS-TMC data. One antenna structure is a so-called dipole antenna structure, having numerous variants thereof, for example a symmetric dipole antenna structure and an asymmetric dipole antenna structure. Wired variants of the symmetric and asymmetric dipole antenna structures comprise a pair of wires, for example flexible wires, constituting a first pole and a second pole. The symmetric antenna structure was originally designed for symmetric Radio-Frequency (RF) input circuits, the symmetric antenna structure simply comprising symmetric twin cables that were connected to an RF receiver. An RF transformer was provided in the RF receiver in order to convert a symmetric antenna signal to an asymmetric antenna signal that could be amplified by a suitable RF amplifier circuit in the RF receiver. Over time, as this technology was developed, a so-called “feedline” was introduced into the design of the antenna for high frequency and/or weak signal applications in order to distance the antenna poles from “noisy” electrical circuitry to which the antenna structure was to be coupled. One type of feedline employed was in the form of a length of coaxial cable. However, the coaxial cable is a transmission line having conductors of unequal impedances with respect to ground potential and so is considered “unbalanced”. In order to match the symmetric impedances (balanced) of the pole wires with the asymmetric impedances of the feedline, it is known to place a so-called “balun” in-line between the pole wires and the feedline, thereby matching the impedances of the pole wires and the feedline and so mitigating unwanted common-mode currents from flowing in the feedline that can cause the pole wires to radiate RF energy.
The so-called dipole antenna structure mentioned above can be employed with varying results in terms of antenna sensitivity. In one further known implementation of the dipole antenna, the wires constituting the first and second poles are arranged so as to extend away from each other in order to provide effective performance.
However, it is desirable to avoid use of the relatively long wires as poles, because the user is burdened with the task of extending and arranging a pair of wires, which can be cumbersome for a user to deploy in a vehicle in order to obtain acceptable levels of antenna sensitivity. Additionally, whilst the level of sensitivity of the above-described antennas is acceptable, it is still nevertheless desirable to increase the sensitivity of the antenna.
One solution to overcome this problem is to dispose the antenna poles in a housing of a mount or docking station or similar accessory for the PND.
In this context, the antenna can be formed with a first solid planar pole and a second solid planar pole. However, when the PND is docked, the antenna located within the housing of the docking station is disposed opposite the PND and in relatively close proximity thereto.
As mentioned above, the PND comprises the GPS antenna to receive satellite broadcast signals relating to GPS data. Typically, the GPS antenna is located within the housing of the PND. Unfortunately, the location of the antenna for receipt of the RDS-TMC data, when formed in the various manners described above, hinders the performance of the GPS antenna due to the proximity of the RDS-TMC antenna located in the docking station or mount to the internal GPS antenna of the PND, thereby hindering receipt of ephemeris data via the GPS antenna.